1. Field of the Invention
The present invention is related to the field of thermal transfer printing and, more particularly, to an improved thermal transfer printhead and a printing system using such a printhead.
2. Description of the Related Art
Thermal transfer printers operate through selective heating of a plurality of microscopic heater elements within the printhead that, when activated, produce points of heat that correspond to each of the dots in an image line that is to be printed on a medium. The heated heater elements, when thereafter brought into contact with the ink on an adjacent ribbon, heat and transfer the ink onto the medium in points or dots corresponding with the dots in the desired image line.
To achieve optimal print quality, the printhead must operate at the correct energy level. Energy level is controlled by modulating both the voltage level applied to the printhead and the length of time that such voltage is applied. In order for the printer to correctly modulate these conditions, it is necessary for the printer to be provided with the average resistance value of the printhead's heater elements and the overall temperature of the printhead. Since, as manufactured, each printhead's heater elements may have a slightly different characteristic resistance value, the manufacturer provides the specific resistance value with each printhead. When the printhead is replaced by the customer, the resistance of the new printhead must be manually entered into the printer control box. Many times, customers do not update the printer resistance value, however, resulting in poor print quality and placing stress on the printing system. In addition, when obtaining new printheads, customers may purchase aftermarket printheads that are inferior to the original printhead obtained with their system. This can also cause poor print quality and, if the replacement printhead is untested or unapproved by the original equipment manufacturer, typically voids any warranty on the printing system due to the negative impact of such printheads on print operation and system performance.
Printhead temperature is monitored on an on-going basis using a sensor located on the printhead printed circuit board (PCB). The temperature reading is transmitted to a printer control box that is separate from the printhead and connected thereto by a cable.
Problems have arisen in that the cable between the control box and the printhead is made up of many wires and therefore is typically thick, expensive and hard to work with. Since all of the wires in the cable have particular purposes, adding new features to the printhead which are to be supported by communication over the cable requires that additional wires be added, making the cable even more cumbersome.
Furthermore, the cable between the printhead and the control box is often of considerable length which, due to electrical noise or other interference, can negatively impact the accuracy and/or update consistency of the temperature measurement that is sent from the printhead to the control box. The conventional temperature sensor used in the printhead PCB produces a small voltage difference between degree increments. This voltage can be more easily affected by electrical noise, etc., when the cable length between the printhead and the control box is lengthy. When the voltage is adversely affected by long cable length, the customer may note that changes in the temperature reading increment by more than one degree between readings. Changes in the temperature reading by more than one degree at a time can give the user the impression that the temperature reading is not very accurate or up to date, reducing customer confidence in the printhead quality even though the difficulty lies in the cable length and not in the printhead itself.
Accordingly, a need exists for an improved thermal transfer printhead that overcomes the foregoing problems in the prior art.